The present applicant has already proposed a device for tightening up nuts on torque-controlled bolts as disclosed in U.S. Pat. No. 4,403,529. This device achieves a high work efficiency but has the drawback of being not usable at locations where a sufficient space is not available for tightening work.
Tightening devices for use with compressed air as a power source are also in use but have the same drawback as above.
FIG. 6 shows a conventional power tightening device, which has two output shafts 17, 18 arranged coaxially and rotatable in opposite directions to each other by a single input shaft 16a through a differential reduction mechanism 16. An inner socket fittable to bolt tips is attached to one of the output shafts, 18, and an outer socket fittable to nuts on bolts is attached to the other output shaft 17.
The differential reduction mechanism 16 generally comprises a multiplicity of planetary gear means, therefore has many parts and is complex in construction. Attempts to compact the differential reduction mechanism are greatly restricted from the viewpoint of machining the parts and the strength thereof, consequently imposing limitations on the size of the case for accommodating this mechanism. Furthermore, the power tightening device is not always usable for fastening structural members. For example, when nuts are to be tightened up by the device 1 with its head 19 inserted in the groove 81 of a channel member 8 as seen in FIGS. 6 and 7, the head 19 is too large to insert into the groove 81.
The present invention provides a device of reduced size for tightening up nuts on torquecontrolled bolts to overcome the above problems. The present device comprises a minimized number of components required for the tightening operation and is made usable as coupled to a conventional power tightening device.
The tightening device of the present invention may be constructed as assembled with the conventional power tightening device, or may be used as removably attached to the conventional device only when required.